Non-woven needled fibrous structure

ABSTRACT

A method of making a web suitable for use as papermakers&#39;&#39; felt including superposing a plurality of fibrous batts such that substantially parallel fibers in one batt extend in transverse direction to substantially parallel fibers in an adjacent batt, needling the superposed batts to form a laminated web, stretching the web to tension the fibers, applying a coating of adhesive to the surface of at least one side of the web, compressing the web, and subjecting the web to a jet of compressed air to break coherent films of the adhesive into globules leaving a portion of the adhesive adhered at points of contact and intersection of fibers on the surface of the web and driving the remaining globules into the web to adhere at points of contact of individual fibers near said surface.

U Umted States Patent 1151 3,664,905

Schuster 14 1 May 23, 1972 [541 NON-WOVEN NEEDLED FIBROUS 1 Reiereneeecited STRUCTURE UNITED sTATEs PATENTS [721 lnvenm" Wilhelm A'lguslsebum" Frankfurt/Maine 2,373,033 4/1945 Kopplin 161/154 x Germany2,961,364 11/1960 Smith et al. ..l6l/l50 x 73 A Filzt h alt-Gesellschaft 't 1 ss'gnee z n a j' FOREIGN PATENTs OR APPLICATIONS 2 iAug. 27 9 9 696,595 10/1964 Canada 161/155 PP 853,362 PrimaryExaminerWilliam A. Powell Related U.S. Application Data Amway-Christensabl [63] Continuation-impart of Ser. No. 512,407, Dec. 8, [57] ABSTRACT1965, abandoned,

A method of making a web suItable for use as papermakers' ForeignApplication P i it D felt including superposing a plurality of fibrousbatts such that substantially parallel fibers in one batt extend Intransverse Feb. 17, 1965 Germany ..F 45271 direction to Substantiallyparallel fibers in an adjacent ban, needling the superposed batts toform a laminated web, [52] U.S. Cl ..161/59, 1 17/62, 1 17/140,Stretching the web to tension the fibers, applying a coating of 156/148156/291 0 adhesive to the surface of at least one side of the web, com-Int Cl B32) 5/06 1332b 5/12 B32b 3/1/22 pressing the web, and subjectingthe web to a jet of com- Fieid 161/55 57 59 pressed air to breakcoherent films of the adhesive into l6l/146148, -158, 156/148, 291, 283;28/722, 74; 117/16, 25, 26, 135.5, 140 R, 62

globules leaving a portion of the adhesive adhered at points of contactand intersection of fibers on the surface of the web and driving theremaining globules into the web to adhere at points of contact ofindividual fibers near said surface.

8 Claims, 8 Drawing Figures Patented May 23, 1972 3,564,905

2 Sheets-Sheet l Patented May 23, 1972 2 Sheets-Sheet 2 FIGB NON-WOVENNEEDLED FIBROUS STRUCTURE This application is a continuation-in-part ofapplication Ser. No. 512,407, filed Dec. 8, 1965, now abandoned.

This invention relates to needled non-woven fibrous structures suitablefor industrial and papermakers felt, and to a method of making suchstructures.

It is known to make so-called synthetic felts by needling fibrous battsof different fibers and subjecting the needled structures to a shrinkingtreatment to increase the coherence and strength thereof. It is alsoknown to bind the fibers of carded or aerodynamically produced webstogether by various means such as impregnation with a latex, adhesivedroplets, partial solution and resolidification of the surface layer,melting of the fibers or use of adhesive fibers.

Another needled fabric structure has been made by subjecting a needledweb or batt first to a shrinking treatment, impregnating the websubsequently with a solution of a bonding agent, treating it, prior tothe evaporation of the solvent, with water, and drying. Such non-Wovenshave been used as such in the textile industry or have been furtherprocessed, for instance, to synthetic leather by coating with a plasticlayer. Attempts to employ such non-wovens in the manufacture of feltsfor use in paper making machines have been without success because suchnon-woven fabrics have had low tensile strength and excessiveelongation.

Conventional papermakers felt includes a woven base which has thepurpose of supporting the surface fleece and imparting to the feltdimensional stability and resistance particularly to tension loads. Inmany respects, the woven base is inconvenient, for instance when theends of a felt, which have been made as a finite piece, must be joinedto an endless belt. In this operation, the drawing of each individualfilament of the fabric base of one end of the felt into the opposite endis tedious and time consuming. The woven base fabric represents acompromise also in other respects. In order to withstand the tensionloads generated in paper making operations, the warps must be strong andthick, and the nap must be sufficiently thick to prevent the base fabricfrom imprinting on the paper sheet being formed.

The art has long sought a base fabric which is free from theabove-recited disadvantages. Recently a base fabric has been used whichconsists of a great number'of parallel fibers to which a fine surfacelayer is needled. However, such felts have not been fully satisfactory.

It is therefore a primary object of the present invention to provideaprocess for making an improved web suitable particularly forpaperrnakers and other industrial felts.

It is a further object of the present invention to provide a strongnon-woven web which is suitable as a papermakers felt.

Other objects and advantages will become apparent from a considerationof the specification and claims.

For a more comprehensive disclosure of the nature, objects andadvantages of the invention, reference is made to the following detaileddescription and to the accompanying drawing, in which:

FIG. 1 is a schematic side view showing a needling apparatus whereby anendless web or felt is needled;

FIG. 2 is an illustration of a felting needle for use in the apparatusof FIG. 1;

FIG. 3 is a fragmentary cross-sectional view showing a felt or webcomprising several layers of fiber pile or batts which have been needledwith the apparatus shown in FIG. 1;

FIG. 4 is a side view of an apparatus for stretching and heatsetting afelt or web produced by the apparatus of FIG. 3;

FIG. 5 is a fragmentary cross-sectional view of the felt of FIG. 3 afterstretching and heat-setting by the apparatus of FIG. 4;

FIG. 6 is a side view of an apparatus for applying a coating to one sideof a stretched felt;

FIG. 7 is an enlarged fragmentary cross-sectional view of a portion ofthe felt of FIG. 5 after being coated with adhesive and subjected to acompressed air jet by the apparatus of FIG. 6; and

FIG. 8 is a view of the felt taken along line 8-8 of FIG. 7.

The strong and dimensionally stable felt, shown in FIGS. 7 and 8 of thedrawing, is obtained without a base fabric or reinforcing structure byfirst superposing several fibrous batts composed of substantiallyparallel oriented fibers in such way that the fibers of the successivesuperposed batts run substantially transverse to each other.Particularly suitable for this purpose are batts having a weight of 20or 150 g. per sq. m. The web composed of such several superposed battsis then needled from one or both sides. The type of needles used, theadvance motion of the fabric, the depth of penetration of the needles,and the number of needle penetrations per square centimeter will dependon the strength of the fibers, on the thickness of the web, and on thedesired aspect of the needled structure.

Referring now more particularly to the drawing for a detaileddescription of the preferred mode of the invention there shown, twocontinuous fibrous batts l0 and 12 each containing substantiallyparallel oriented fibers are produced by two card apparatus, not shown.The batts are superposed such that one fibrous batt, for example lowerbatt 10 of FIG. 1, consists of fibers oriented substantiallytransversely of the running direction of the card apparatus and thebatt, and the other batt, for example upper batt 12, consists of fibersoriented substantially longitudinally to the running direction of thecard and the batt. Preferably, the longitudinally running fibers arestronger, e.g., l2 denier, than the transversely running fibers, e.g., 6denier, since the felt structure will later preferably be stretched inthe direction of the longitudinally running fibers.

In one preferred embodiment, the transversely running fibers are staplepolyamide fibers (nylon 66) of 6 denier and a tensile strength of about5 g./den. and about mm. in length. They are a substantially round crosssection and are essentially crimped. The stronger longitudinally runningfibers Y are preferably polyester fibers, have an essentially roundcross section, are essentially smooth or stretched and have a tensilestrength of about 10 g./den. These fibers also are staple fibers.

In another embodiment, the transversely running fibers may be naturalfibers such as wool or cotton. Alternatively, up to 30 percent by weightof natural fibers may be admixed with the synthetic fibers in theindividual fibrous batts as they are produced and superposed.

While polyamide fibers such as the nylons are preferred asthetransversely running fibers, other fibers may be used includingpolyester fibers, e.g., polyethylene terephthalate, polyacrylonitrilefibers and aromatic polyamide fibers. The thickness of these fibers mayvary from 6 to 60 denier and the staple lengths may vary from 50 to I40mm..Polyester fibers are preferably used for the longitudinally runningfibers while other operable fibers include polyamide fibers such asnylon and aromatic polyamide fibers. The thickness of the longitudinallyrunning fibers may range from 12 to 60 denier and their staple lengthfrom 80 to mm. Preferably the thickness is greater than that of thetransversely running fibers.

Referring particularly to FIG. 1, fibrous batts 10 and 12 are fedautomatically by feeding table 14 into needling apparatus 16 betweensupport 18 and needling loom 20 which contains 3 needles per squarecentimeter and are pieced by needles 22 provided with barbs 24 (see alsoFIG. 2) to at least partially intermingle the fibers of the two battsand form a laminated web 26. The web which emerges from needlingapparatus 16 is thinner than the superposed batts l0 and 12 due to theneedling operation. If a thicker web is desired, web 26 is guided aroundrolls 28 and 30 in accordance with the directional arrow in FIG. 1 andis reintroduced into needling apparatus 16 beneath additional fibrousbatts l0 and 12 and this is continued until the desired thickness isachieved. This procedure results in an endless web of felt. It is to beunderstood, however, that webs of any desired length may also beproduced. In addition, needling of the web may be continued to furtherreduce the thickness and/or increase the density thereof after ceasingaddition of batts 10 and 12.

The web of felt is needled with needles 22 and it has been found thatupon six passages of the web through apparatus 16, a total number of 360penetrations per square centimeter will be achieved. If desired, the webmay be inverted and needled on the reverse side. Two passages of theinverted web through apparatus 16 will result in 120 penetrations persquare centimeter on the reverse side thereof.

The needled felt shown in FIG. 3 was produced in accordance with theabove procedure with the modification that after two passages of web 26through apparatus 16, introduction of batt was ceased while introductionof batt 12 was continued for one more passage so that the completed feltwas provided with both outer layers containing substantiallyIongitudinally running fibers. Thus, in FIG. 3, layers A, C and Econtain substantially longitudinally running fibers and were formed frombatt 12, while layers B and D contain substantially transversely runningfibers and were formed from batt 10. The successive layers A E aretherefore arranged in a manner that the fibers of each layer runsubstantially transversely to the fibers of the next successive layer.

After needling of endless web 26, it is strongly stretched in order toplace a large portion of the interlooped fibers under tension andfurther orienting them in the direction of the applied stretch; theamount of said stretch will depend, to a certain extent, on the natureof the fibers.

Referring now to FIG. 4, there is shown schematically a stretchingapparatus 32 for stretching and, if desired, heatsetting web 26 producedin accordance with the above teaching with regard to the apparatus shownin FIG. 1. Web 26 is arranged around calendar 34 and small roller 36.Calendar 34 may be heated by means not shown if it is desired toheat-set web 26 in the tensed state. The temperature of heating willvary depending on the fibers present in the web and will generally rangebetween 120 and 190 C. In any event, the temperature should not exceedthe melting point of the lowest melting fiber which is resent. Thedistance between calendar 34 and roller 36 and thus the tension on web26, is variable by moving roller 36, for example, in guide rails, notshown, in which roller 36 may be mounted and fixed at any desireddistance from calendar 34. Web 26 is fed around calendar 34 and roller36 by rotation of calender 34 in accordance with the directional arrowthereon in FIG. 4. Ten sion placed on web 26 will vary according to thefibers used therein and will generally range between 50 and 1,000 kg.per meter width ofthe web.

FIG. 5 shows an enlarged partial section through web 26 after treatmenton stretching apparatus 32. Layers A E correspond to the same layers inFIG. 3. It will be seen that the fibers and particularly those in layersA, C and E, are even more oriented in the longitudinal direction thanare those in the felt of FIG. 3.

For further reinforcement, the web 26 is then bonded on one or bothsurfaces by means of a water-insoluble elastic adhesive, such as asolution of butadiene-acrylonitrile or 2- chlorobutadiene, in such a waythat water can pass freely through the felt. Procedures used heretoforeare not generally suitable for application of the adhesive according tothe present invention. For example, when applied by spray nozzles, theadhesive does not penetrate the web or felt sufficiently; if applied byan immersion or impregnation procedure, the depth of the penetration ofthe adhesive cannot be controlled. Therefore, if the felt made accordingto the invention as set forth hereinabove is to be used as papermakersfelt, it is coated on only one side with a water-insoluble elasticadhesive layer of even thickness; subsequently the coated felt iscompressed and then treated on the coated surface with a strong jet ofcompressed air. Thereby, films or membranes which may have been formedby the adhesive which still contains the solvent, are broken up, and theadhesive is distributed on and near the surface of the felt in such away that after releasing the compression pressure and after thetreatment with the compressed air, adhesive remains only on theindividual fibers and particularly at their points of contact.

Only as much adhesive must be applied that only the fibers of one orboth surface layers are bonded while the fibers in the interior of theweb remain essentially free of adhesive. The total pickup of adhesivewill be in the range of l to 15 percent of weight of the finished felt.

While butadiene-acrylonitrile and 2-chlorobutadiene have been recited aspreferred adhesives, other operable adhesives include polyurethaneelastomers, modified polyester resins and polyacetals. Compatiblemixtures of the above adhesives may also be used. The adhesive maycontain a solvent for purposes of adjusting the viscosity to be suitablefor application by applicator roll coating or other means. Such solventsinclude ethyl acetate, methyl ethyl ketone, isopropyl alcohol, xylol,ethylene glycol diacetate, and mixtures thereof.

The adhesive may be applied to the felt by any conventional method,e.g., by a doctor blade, or by running the felt over or betweenapplicator rolls. The mechanical compression of the felt is then alsocarried out in any suitable manner, e.g., by means of two rollersrotating in opposite directions, thereby binding the adhesivelycoatedfibers at additional points of contact.

In order to shorten the drying time of the felt to which the adhesivehas been applied, compressed air of slightly elevated temperature may beemployed. Instead of, or in addition to, the compression treatment afterapplication of the adhesive, the felt may be subjected to suchcompression treatment after the compressed air treatment but before theadhesive is completely dried.

In a preferred embodiment of the invention, a needled felt of thecharacter described hereinabove is compressed between two superposedmetal rollers the lower one of which carries an adhesive layer kept at aconstant thickness by means of a doctor; the adhesive penetrates thelower surface of the felt and envelops the fibers. When the felt hasleft the rollers, the fibers coil back into their original bulkyposition. The adhesive membranes left between many of the fibers arethen torn by means of strong compressed air jets whereby a portion ofthe adhesive remains especially at the points of contact andintersection of the fibers at the surface of the felt and the adhesiveis broken into globules which are driven by the air jets further intothe web until they contact and are stopped by points of contact of otherfibers near the surface.

FIG. 6 illustrates schematically an apparatus 38 for coating web 26after it has been stretched. Web 26 is first fed between rollers 40 and42 which are arranged to compress the web, e.g., to about one-half itsthickness in the relaxed state. Roller 42 is suspended in pan 44 whichcontains an elastomeric adhesive 46 and as roller 42 rotates therein, itpicks up a layer 48 of adhesive 46, the thickness of which is controlledby doctor 50. When the surface of roller 42 reaches web 26, the layer 48of adhesive 46 is transferred to surface 52 of web 26. The adhesive isthen pressed by the compressive strength of rollers 40 and 42 betweenthe fibers on surface 52 of the web. Web 26 is then guided around roll54 at which time surface 52 is subjected to the action of one or morecompressed air jets 56 which flow under a pressure of from 2 to 8atmospheres from nozzles 58. The strong jets 56 of compressed air will,first of all, rupture the thin film of adhesive between the individualfibers and, in addition, drive the resulting globules of adhesive intoweb 26 where they will contact and adhere to points of contact ofindividual fibers near the surface thereof. After the major proportion,e.g., from to 100 percent, of the solvent has evaporated or been drivenfrom the adhesive, web 26 is fed between compressive rollers 60 and 62wherein it is strongly compressed at a pressure from 2.5 to 12 kg. percm. width of the web.

The thickness of layer 48 of adhesive may range from 0.2 to 1.5 mm. Witha preferred thickness of 0.4 mm., web 26 will take up about percent ofthe adhesive carried by roller 42. The depth of penetration of theadhesive into surface 52 of web 26 depends on the pressure extendedbetween rollers 40 and 42. For example, when a web having a thickness of5 mm. in the relaxed state is compressed to 2.5 mm. by rollers 40 and42, web 26 upon emerging from the rollers and relaxing to its originalthickness of 5 mm. will have adhesive penetrating to from 1 to 1.5 mm.into surface 52.

FIGS. 7 and 8 illustrate a portion of web 26 after the web has emergedfrom coating apparatus 38 shown in FIG. 6. It will be seen that discreteparticles or globules 64 of adhesive are adhered to several of thefibers 66 and particularly at points of intersection of the fibers bothat surface 52 and near the surface ofthe web.

The following is presented as a specific example of a preferredembodiment of the present invention.

Two continuous fibrous batts containing substantially parallel orientedfibers were superposed so that fibers of the lower batt were orientedsubstantially transversely of the running direction of the batt and thefibers of the upper batt were oriented substantially longitudinally orparallel to the running direction of the batt. The fibers of the lowerbatt were crimped staple fibers of 6 denier polyamide (nylon 66) havinga tensile strength of about 5 g./den. and an average length of about 80mm. The fibers of the upper batt were smooth uncrimped fibers of i2denier polyester (polyethylene terephthalate) having a tensile strengthof about 10 g./den. and an average length of about 80 mm. The superposedfibrous batts were fed into a needling machine and subjected to theaction of a needling loom containing two barbed needles/sq. cm. Theemerging laminated web was reintroduced into the needling apparatusbeneath two additional fibrous batts to form a continuous, endless web.After two complete passages of the web through the needling apparatus,introduction of the lower batt was ceased while introduction of theupper batt was continued for one more passage so that the completed webof five layers contained two outer layers of substantiallylongitudinally running fibers. After a total of six passages through theneedling apparatus, a total number of 360 penetrations/sq. cm. of webwas achieved. The web was then turned and needled on the reverse side intwo passages through the machine to achieve 120 penetrations/sq. cm. onthe reverse side.

The web, having a thickness of about 5 mm., was then arranged around alarge heated calender and a smaller roller, the latter being movablymounted to vary the distance between the calendar and the roller. Atension of 280 kg. per meter width was placed on the web and thecalender was heated to a temperature of 150 C. to heat-set the tensedfibers.

The web was removed from the calendar and roller and then fed betweentwo compression rollers, the lower of which was suspended in anelastomeric adhesive comprising 20 weight percentbutadiene-acrylonitrile dissolved in 70 weight percent ethyl acetate and10 weight percent methyl ethyl acetone. The thickness of adhesive pickedup by the roller was controlled to be about 0.4 mm. As the surface ofthe roller carrying the adhesive contacted the web, about 95 percent ofthe adhesive was transferred to the web surface. As the coated webpassed between the rollers, it was compressed to a thickness of about2.5 mm. and the adhesive was pressed between the fibers on the surfaceof the web. After the web had again relaxed to a thickness of about 5mm., it was found that the adhesive had penetrated to a depth between 1and 1.5 mm. from the coated surface. The adhesive coated surface of theweb was then subjected to the action of the air under a pressure ofabout 6 atmospheres to break the continuous film of adhesive intodiscrete particles or globules. A portion of the globules remainedadhered to the fibers and to points of contact and intersection thereofon the surface of the web and the remaining globules of adhesive weredriven into the web where they became adhered to fibers and points ofcontact thereof near the surface. After 90 percent of the solvent hadevaporated from the adhesive, the web was passed between a second pairof compressive rollers and compressed at a pressure of 4 kg. per cm.width of the web.

Wet felts prepared in accordance with the present invention have aconsiderably higher breaking strength than conventional felts of thesame wei ht per square foot. When used in papermaking machines, t eylose substantially no fibers.

Marking does not occur due to the lack of a woven base fabric. The novelfelts have a much longer life than conventional papermakers felts.

With a felt produced according to the present invention, running timesup to days of 24 hours each can be achieved on a papermaking machine. Onthe other hand, felts produced in in the traditional manner achievemaximum running times. as a rule, of only about 30 days. The suctioncapacity of felt produced according to the present invention is in noway inferior to that of felt produced in the traditional manner. Itslong, useful life can be explained by the fact that, through the coatingwith adhesive, the loss of fiber is reduced to a minimum. At the sametime, the felt is given a decided stability of form by the presentprocess.

The loss of fiber from felt produced according to the present inventionis so small that paper for electronic condensers can be producedthereon. The requirements for purity of such a paper are so great thatpaper produced on customary felts could not previously be used for thispurpose since the loss of fiber occurring with use of traditional feltsinfluenced the dielectric constant in an unfavorable way.

In felts used in the papermaking process, it has been found of advantageto use blends of natural and synthetic fibers in order to combine thegood properties of both. Accordingly, such blends can also be used forthe making of the felts according to the invention, or batts ofdifferent fibers may be used. In the latter case, it is of advantage toplace the batts composed of the stronger fibers in such a way that saidfibers are in the longitudinal or stretching direction of the finishedfelt, so that the stretching step tends to maintain a larger portion ofthe fibers in tension and oriented in the stretching direction.

What is claimed is:

l. A method of making a laminated fibrous web which comprises:superposing a plurality of fibrous batts, each of said batts havingfibers oriented substantially in parallel and the batts being superposedso that the fibers in one batt extend transverse to the fibers in anadjacent batt; needling the superposed batts to form a laminated web;stretching the web; applying a coating of adhesive to the surface of atleast one side of said web; and subjecting the coated surface of the webto a jet of compressed air to break coherent films of said adhesive.

2. The method according to claim 1 wherein batts of different fibercomposition are employed.

3. The method according to claim 2 wherein batts containing strongerfibers are arranged so that said fibers are oriented in the direction inwhich the web is stretched.

4. The method according to claim 1 wherein at least one batt contains ablend of material and synthetic fibers.

5. The method according to claim 1 wherein the web is compressed afterthe adhesive coating is applied thereto.

6. The method according to claim 1 wherein the web is compressed aftersubjection to compressed air and before the adhesive is completely dry.

7. The-method according to claim 1 wherein the adhesive is applied in alimited amount to form bonds between fibers on and near the coatedsurface only of the web.

8. A laminated fibrous web product according to the method of claim 1.

2. The method according to claim 1 wherein batts of different fibercomposition are employed.
 3. The method according to claim 2 whereinbatts containing stronger fibers are arranged so that said fibers areoriented in the direction in which the web is stretched.
 4. The methodaccording to claim 1 wherein at least one batt contains a blend ofmaterial and synthetic fibers.
 5. The method according to claim 1wherein the web is compressed after the adhesive coating is appliedthereto.
 6. The method according to claim 1 wherein the web iscompressed after subjection to compressed air and before the adhesive iscompletely dry.
 7. The method according to claim 1 wherein the adhesiveis applied in a limited amount to form bonds between fibers on and nearthe coated surface only of the web.
 8. A laminated fibrous web productaccording to the method of claim 1.